<template>
  <div>
    我是sond子组件----{{ num }}
    <button @click="btnClick">修改num</button>
  </div>
</template>
<script>
export default {
  props: {
    num: {
      type: Number
    }
  },
  methods: {
    btnClick() {
      this.$emit('update:num', this.num + 1)
    }
  }
}
</script>
<style>
</style>
